TWI818527B - Conductive film for high frequency circuit board and high frequency circuit board - Google Patents

Abstract

The present invention provides a conductive film for high-frequency circuit boards, which sequentially includes: a base material, an adhesion layer disposed on at least one side of the base material, and a copper layer disposed above the adhesion layer, wherein at 10 GHz At the measurement frequency, the relative permittivity of the base material is below 3.3, and the adhesion layer includes a nickel-copper alloy.

Description

Conductive diaphragms for high-frequency circuit boards and high-frequency circuit boards

The present invention relates to a conductive film for a high-frequency circuit board and a high-frequency circuit board.

Now, mainly with the standardization of fifth-generation mobile communications (5G), conventional signals need to be transmitted in higher frequency fields. In order to take advantage of the advantages of 5G (ultra-high speed, ultra-low latency, multiple simultaneous connections), signals need to be transmitted in the quasi-millimeter wave field.

In the past, flexible printed circuit boards (FPCs) based on polyimide substrates were used as circuit boards. Their transmission losses were large, making it difficult to apply circuit boards to signal transmission in the quasi-millimeter wave field. Therefore, compared with polyimide, a substrate with lower relative permittivity and loss tangent (low dielectric material) is required as the base FPC.

In addition, in the future, not only the quasi-millimeter wave field, but also the higher frequency frequency field (millimeter wave field) will be considered. In addition, the sixth generation mobile communication standard (6G) has been discussed, and the utilization of the 100GHz~1000GHz (1THz) field in 6G is also being considered.

From the above background, it is necessary to use flexible copper foil laminates (FCCL) with low dielectric materials and small transmission loss.

[Prior technical literature] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2018-160636.

Patent Document 1 discloses a substrate for high-frequency signal high-speed transmission that uses a group of chromium, nickel, and nickel-chromium alloy as the base layer in order to improve the adhesion between a substrate with a low permittivity and a copper layer. However, in the technology disclosed in Patent Document 1, although the adhesion between the base material and the copper layer is good, there is a problem of poor etching properties during circuit formation.

The present invention solves the above-mentioned various problems of the conventional art and achieves the following objects as a subject. That is, an object of the present invention is to provide a conductive film for high-frequency circuit boards and a high-frequency circuit board that have low transmission loss and good adhesion and etching properties between the base material and the copper layer.

As a means to solve the aforementioned problems, the following is described. That is:

<1> A conductive film for high-frequency circuit boards, characterized by comprising in order: a base material; an adhesion layer provided on at least one side of the base material; and a copper layer provided above the adhesion layer; wherein , at a measurement frequency of 10 GHz, the relative permittivity of the base material is less than 3.3; the adhesion layer is made of nickel-copper alloy.

<2> The conductive film for high-frequency circuit boards as described in the aforementioned <1>, the aforementioned base material includes cycloolefin polymer resin, polyphenylene sulfide resin, polystyrene resin, fluororesin and polyether ether ketone resin At least any of them.

<3> The conductive film for high-frequency circuit boards according to any one of the above <1> or the above <2>, wherein the adhesion strength of the interface between the base material and the adhesion layer is 0.5 N/mm or more.

<4> A high-frequency circuit board, characterized by comprising in order: a base material; an adhesion layer provided on at least one side of the base material; and wiring provided above the adhesion layer; wherein, measurement at 10 GHz At frequency, the relative permittivity of the base material is below 3.3; the adhesion layer includes nickel-copper alloy.

According to the present invention, many of the above-mentioned problems of the conventional art can be solved, the above-mentioned objects can be achieved, and a conductive film for high-frequency circuit boards and high-frequency circuits with low transmission loss, good adhesion and etching properties between the base material and the copper layer can be provided. plate.

10: Conductive diaphragm for high frequency circuit boards

11:Substrate

12:Adhesion layer

13: Copper layer

14:Wiring

15: Oxidation prevention layer

16: Anti-rust layer

20:High frequency circuit board

[Fig. 1] Fig. 1 is a cross-sectional view showing an example of a conductive film for a high-frequency circuit board of the present invention; [Fig. 2A] Fig. 2A is a cross-sectional view showing an example of a high-frequency circuit board of the present invention; [Fig. 2B ] Figure 2B is a cross-sectional view showing another example of the high-frequency circuit board of the present invention; [ Figure 2C ] Figure 2C is a cross-sectional view showing another example of the high-frequency circuit board of the present invention; [ Figure 2D ] Figure 2D is a cross-sectional view showing the present invention. Cross-sectional view of another example of the high-frequency circuit board of the invention; [Fig. 3] Fig. 3 is a diagram showing an example of the relationship between transmission loss and frequency in Examples 1 to 4 and Comparative Examples 1 to 2.

(Conductive diaphragm for high frequency circuit boards)

The conductive film for high-frequency circuit boards of the present invention sequentially includes: a base material, an adhesion layer provided on at least one side of the base material, and a copper layer provided above the adhesion layer, wherein at 10 GHz At the measurement frequency, the relative permittivity of the base material is 3.3 or less. The adhesion layer includes a nickel-copper alloy and, if necessary, further includes other layers.

In the case of wireless communication in the present invention, frequencies above 10 kHz are generally referred to as high frequencies.

<Substrate>

The aforementioned base material is the substrate of the conductive film for high-frequency circuit boards of the present invention, and is also a material whose relative permittivity is 3.3 or less at a measurement frequency of 10 GHz.

Transmission losses in signal transmission can generally be divided into three causes: dielectric loss, conductor loss and other losses. Among them, the aforementioned dielectric loss is shown in the following formula 1, which is represented by a function of the relative permittivity of the base material and the loss tangent. The greater the relative permittivity or the loss tangent, the greater the dielectric loss will be. Therefore, in order to reduce the loss tangent, it is preferable to use a base material that is lower than the aforementioned relative permittivity and lower than the aforementioned loss tangent. By using a base material with a lower relative permittivity than the above and a lower loss tangent than the above, a conductive film for a high-frequency circuit board with less transmission loss can be obtained.

The above symbols are expressed as: ε: relative permittivity, f: frequency, C: speed of light, tanδ: loss tangent.

-Relative permittivity-

The relative permittivity of the base material is 3.3 or less, preferably 3.1 or less, more preferably 2.5 or less.

The relative permittivity of the aforementioned substrate was measured at a frequency of 10 GHz based on the resonant cavity method based on JIS R1641.

-loss tangent-

The aforementioned loss tangent preferably has a value of 0.005 or less, more preferably 0.003 or less, and more preferably 0.001 or less.

The loss tangent of the aforementioned substrate was measured at a frequency of 10 GHz based on the resonant cavity method based on JIS R1641.

The shape, structure and size of the base material are not particularly limited and can be appropriately selected depending on the purpose.

Examples of the material of the base material include cycloolefin polymer resin, polyphenylene sulfide resin, polystyrene resin, fluororesin, polyether ether ketone resin, and the like. These materials may be used individually by 1 type, or 2 or more types may be used together. By using these materials as the base material, a conductive film for high-frequency circuit boards with less transmission loss can be obtained.

The average thickness of the base material is preferably from 6 μm to 300 μm , preferably from 12 μm to 250 μm , and more preferably from 25 μm to 200 μm . When the average thickness of the base material is 6 μm or more, the handleability and bendability during processing can be improved. In addition, when the average thickness of the base material is 300 μm or less, a flexible conductive film for high-frequency circuit boards can be obtained. The optimal thickness of the average thickness of the base material varies depending on the application. In fields that require thinner films and higher flexibility, the average thickness of the base material is required to be close to 6 μm . In addition, there are also applications that require the average thickness of the base material to be close to 300 μm in terms of insulation, high reliability, and circuit formation methods.

The average thickness of the base material was obtained by measuring the thickness at 5 points using an electronic micrometer (manufactured by Anrichi Co., Ltd., equipment name: KG3001A) and calculating the average value.

In addition, regarding the conductor loss among the transmission losses in signal transmission, as shown in the following equation 2, the conductor loss is expressed as a function of resistivity and magnetic permeability. In the high-frequency field, due to the influence of the skin effect, current will only flow on the surface of the conductor, and the unevenness of the interface between the substrate and the conductor has a great impact on signal transmission. Therefore, the smoothness of the interface between the base material and the conductor is very important. The smaller the unevenness of the interface, the smaller the resistivity will be and the smaller the conductor loss will be. In order to suppress transmission losses in high-frequency circuit boards, not only dielectric losses but also conductor losses must be considered.

The above symbols are expressed as: f: frequency, μ: magnetic permeability, ρ: resistivity.

Examples of indicators of the smoothness of the base material include the arithmetic mean roughness Ra of the surface of the base material and the maximum height Rz of the surface of the base material.

The arithmetic mean roughness Ra of the surface of the base material is preferably 500 nm or less, more preferably 400 nm or less, and more preferably 300 nm or less. When the arithmetic mean roughness Ra of the surface of the base material is 500 nm or less, a conductive film for a high-frequency circuit board with low transmission loss can be obtained.

The arithmetic mean roughness Ra of the surface of the base material was measured using an optical interference surface roughness meter (WYKO ContourGT K1M, manufactured by Bruker Japan Co., Ltd., measurement conditions: VSI mode).

The maximum height Rz of the surface of the substrate is preferably 5000 nm or less, more preferably 3000 nm or less, more preferably 2000 nm or less.

The aforementioned maximum height Rz refers to the average of the first 10 maximum values among the values separated by the top and bottom of the measurement surface.

The maximum height Rz of the surface of the aforementioned base material was measured using a light interference surface profile roughness meter (WYKO ContourGT K1M, manufactured by Bruker Japan Co., Ltd., measurement conditions: VSI mode).

Although the transparency of the substrate is not particularly limited, when the conductive film for high-frequency circuit boards of the present invention is used in devices requiring transparency such as transparent displays and transparent antennas, the one with the highest transparency (transmittance, haze) is good.

The transmittance of the aforementioned base material is preferably above 60%, more preferably above 70%, and more preferably above 80%.

The haze of the aforementioned base material is preferably 10% or less, more preferably 8% or less, and more preferably 6% or less.

The aforementioned transmittance and the aforementioned haze were measured using a haze meter (manufactured by Nippon Denshoku Industry Co., Ltd., equipment name: NDH5000SP) in accordance with JIS K7361-1 and JIS K7136 respectively.

Although there are no special restrictions on the transmittance and haze of the aforementioned substrate, when the flexible printed circuit board (FPC) is placed on a transparent device or module, it is also required to make the FPC inconspicuous, and by using a transmittance of 60% or more, 10 Substrates with a haze below % make the FPC itself inconspicuous. In addition, in fields requiring higher transparency, high transparency and low haze are required. In this case, transmittance is required: 80% or more and haze: 6% or less.

<Adhesion layer>

The adhesion layer is a layer disposed on at least one side of the base material. The adhesion layer is a layer disposed between the base material and the copper layer to be described later, and is a carrier layer having the function of firmly adhering the copper layer to be described later and the base material.

The aforementioned adhesion layer contains a nickel-copper alloy, and if necessary, further contains other components. Since the adhesion layer contains a nickel-copper alloy, a conductive film for high-frequency circuit boards with excellent etching properties and adhesion can be obtained.

The copper content in the nickel-copper alloy as the adhesion layer is preferably 32 mass% or more and 67 mass% or less relative to the total amount of nickel and copper in the adhesion layer, and 32 mass% or more and 56 mass% The following is preferred, 32 mass % or more and 45 mass % or less is more preferred, and 32 mass % or more and 40 mass % or less is most preferred.

Regarding the composition of the adhesion layer, by setting the proportion of copper to 32% by mass or more relative to the total amount of nickel and copper in the adhesion layer, it is no longer a ferromagnetic material at room temperature and the magnetic permeability can be reduced. Therefore, the influence of skin effect can be reduced. In addition, by setting the proportion of copper to 67 mass % or less relative to the total amount of nickel and copper in the adhesion layer, the adhesion of the interface between the base material and the adhesion layer can be improved, and by setting it to 40 mass % or less, it can be further improved. Further improve adhesion.

The content of nickel in the nickel-copper alloy as the above-mentioned adhesion layer is preferably 33 mass % or more and 68 mass % or less, relative to the total amount of nickel and copper in the above-mentioned adhesion layer. It is preferably 44 mass % or more and 68 mass %. The following is preferred, 55 mass % or more and 68 mass % or less is more preferred, and 60 mass % or more and 68 mass % or less is most preferred.

As for the material of the above-mentioned adhesion layer, if the content of nickel and copper is more than 90% by mass relative to the total amount of the material of the adhesion layer, the present invention is not particularly limited as long as the effect of the present invention can be exerted, and it can be based on Purpose has other ingredients as appropriate.

The shape, structure, and size of the aforementioned adhesion layer are not particularly limited and can be appropriately selected depending on the purpose.

There are no particular restrictions on the other components mentioned above. As long as the effect of the present invention is not hindered, components other than nickel-copper alloy may be appropriately included.

The average thickness of the adhesion layer is preferably from 3 nm to 100 nm, preferably from 4 nm to 50 nm, more preferably from 5 nm to 25 nm. The average thickness of the aforementioned adhesion layer is 3nm When it is above, adhesion can be improved, and when it is below 100nm, productivity can be improved. In addition, the electrical conductivity of nickel alloy is worse than that of copper. When the average thickness of the adhesion layer is more than 100nm, it may affect signal transmission. In addition, the average thickness (height) of the aforementioned adhesion layer was measured as follows.

First, a circuit board is prepared, and a plurality of adhesion layers with a specific thickness are formed on the circuit board. The physical film thickness of the adhesion layers with a specific thickness is measured using a contact profilometer. Next, through quantitative analysis using a fluorescence X-ray measurement device (XRF), the amount of the adhesion layer material in the adhesion layer with a plurality of specific thicknesses is measured. The aforementioned film thickness measured by a contact profilometer and the amount of adhesion layer material measured through quantitative analysis using a fluorescent X-ray measuring device (XRF) were used to create a calibration line. In the actual sample to be measured, the amount of the adhesion layer material is quantitatively analyzed using a fluorescent X-ray measurement device (XRF), and the film thickness is calculated using the prepared calibration curve. Similarly, make 10 samples and take the average value as the average thickness.

The adhesion strength (N/mm) of the base material and the adhesion layer is preferably 0.5 N/mm or more, more preferably 0.6 N/mm or more, and more preferably 0.7 N/mm or more. When the adhesion strength between the base material and the adhesion layer is 0.5 N/mm or more, a circuit can be formed without peeling off the base material and the adhesion layer during resist coating or patterning during circuit formation. In addition, if it is necessary to further form fine circuits, an adhesion strength of 0.5N/mm or more is preferred.

Examples of methods for forming the adhesion layer include various sputtering methods, vacuum evaporation methods, ion plating methods, and the like, including DC magnetron sputtering using nickel-copper alloy as a material. Overall surface method, etc.

<Copper Layer>

The copper layer is a layer disposed above the adhesion layer. The copper layer is disposed on at least a surface of the adhesion layer opposite to the surface facing the base material.

The shape, structure, and size of the copper layer are not particularly limited and can be appropriately selected depending on the purpose.

As for the material of the copper layer, if the content of copper is 95% by mass or more relative to the total amount of the material of the copper layer, the present invention is not particularly limited as long as the effect of the present invention can be exerted, and it can be appropriately determined according to the purpose. Earth has other ingredients.

The average thickness of the aforementioned copper layer is preferably from 0.05 μm to 5 μm , preferably from 0.06 μm to 3 μm , and more preferably from 0.07 μm to 2 μm . When the average thickness of the copper layer is 0.05 μm or more, the film can be thickened by post-processing copper electrolytic plating after forming the copper layer as a seed layer; if it is 5 μm or less, it is possible to form a highly productive product. copper layer.

In addition, the average thickness (height) of the aforementioned copper layer is measured as follows.

First, a circuit board is prepared, and a plurality of copper layers with a specific thickness are formed on the circuit board. The physical film thickness of the plurality of copper layers with a specific thickness is measured using a contact profilometer. Next, through quantitative analysis using a fluorescent X-ray measurement device (XRF), the amount of copper layer material in a plurality of the aforementioned copper layers with specific thicknesses is measured. The aforementioned film thickness measured by a contact profilometer and the amount of copper layer material measured through quantitative analysis using a fluorescent X-ray measuring device (XRF) were used to create a calibration line. In the actual sample to be measured, a fluorescent X-ray measurement device (XRF) is used to quantitatively analyze the amount of copper layer material, and the film thickness is calculated using the prepared calibration line. Similarly, make 10 samples and take the average value as the average thickness.

In addition, in other aspects, the average thickness of the aforementioned copper layer is preferably from 0.05 μm to 40 μm , more preferably from 0.05 μm to 25 μm , more preferably from 0.05 μm to 18 μm . . When the average thickness of the copper layer is 40 μm or less, a circuit equivalent to a base material with copper foil used for general circuit formation can be formed.

In addition, the average thickness of the copper layer described later can be determined by, for example, the average of 10 or more values (parts) of the thickness of the copper layer in a cross-sectional image taken in a direction orthogonal to the surface direction of the substrate. Find out.

As a method for forming the copper layer with an average thickness of 0.05 μm or more and 5 μm or less, for example, various sputtering methods, vacuum evaporation methods, ion deposition methods, and DC magnetron sputtering methods using copper as a material are used. Examples of the electroplating method include methods of treating at least the entire surface of the adhesion layer opposite to the surface facing the base material.

Examples of a method for forming the copper layer having an average thickness of 0.05 μm to 40 μm include electrolytic copper plating.

<Other layers>

The aforementioned other layers are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include an oxidation prevention layer and the like.

<<Oxidation prevention layer>>

The oxidation prevention layer is a layer disposed on a surface of the copper layer opposite to the surface facing the adhesion layer.

The shape, structure, and size of the aforementioned oxidation prevention layer are not particularly limited and can be appropriately selected depending on the purpose.

Examples of the material of the oxidation prevention layer include metals including at least one of nickel, chromium, silicon, zinc, silver, gold, and aluminum, oxides, and nitrides.

The average thickness of the aforementioned oxidation prevention layer is preferably from 0.001 μm to 5 μm , and more preferably from 0.002 μm to 3 μm .

Examples of methods for forming the oxidation prevention layer include various metals and alloys as materials, various sputtering methods represented by DC magnetron sputtering, vacuum evaporation, ion plating, and others. Electrolytic plating, electroless plating, wetland coating, immersion coating, spray coating Examples include methods of forming the entire surface of the copper layer opposite to the surface facing the adhesion layer.

The conductive film for high-frequency circuit boards of the present invention includes, in order, the aforementioned base material, the aforementioned adhesion layer, the aforementioned copper layer, and the aforementioned other layers.

Here, an example of the conductive film for high-frequency circuit boards of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of the conductive film for high-frequency circuit boards of the present invention.

The conductive film 10 for high-frequency circuit boards shown in FIG. 1 includes an adhesion layer 12 and a copper layer 13 on a base material 11 in this order.

Examples of applications of the conductive film for high-frequency circuit boards of the present invention include antenna-related applications such as 5G base stations, millimeter-wave radars, and various antennas. Lists those related to high-speed communication FPC such as smartphones, tablet devices and servers.

(High frequency circuit board)

The high-frequency circuit board of the present invention includes, in order, a base material, an adhesion layer provided on at least one side of the base material, and wiring provided above the adhesion layer, wherein at a measurement frequency of 10 GHz, The relative permittivity of the base material is 3.3 or less. The adhesion layer includes a nickel-copper alloy and, if necessary, further includes other layers.

In the high-frequency circuit board of the present invention, the base material and the adhesive layer are the same as those described in the conductive film for high-frequency circuit boards of the present invention.

<Wiring>

The wiring is arranged on a surface of the adhesion layer opposite to a surface facing the substrate.

The shape of the wiring is not particularly limited and can be appropriately selected depending on the purpose. For example, a cross-section orthogonal to the longitudinal direction may be approximately a quadrilateral or the like.

There is no particular limitation as to the structure of the aforementioned wiring, and can be appropriately selected depending on the purpose.

As for the material of the wiring, if the content of copper is 95% by mass or more relative to the total amount of the wiring material, the present invention is not particularly limited as long as the effect of the present invention can be exerted, and can be appropriately selected according to the purpose. .

As an example of the size of the wiring, the line width of the wiring is preferably 50 μm or less, more preferably 40 μm or less, and more preferably 30 μm or less. When the line width of the wiring is 50 μm or less, the circuit board can be miniaturized and the applied semiconductor device can be miniaturized. In addition, the average thickness (height) of the wiring is not particularly limited as long as it is a thickness that can exert its function, and can be appropriately selected according to the purpose. For example, the thickness is 1.0 μm or more and 40 μm . The following is preferred, preferably 1.5 μm or more and 25 μm or less, more preferably 2.0 μm or more and 18 μm or less. In addition, the average thickness (height) of the wiring may be, for example, 10 or more of the thickness (height) of the wiring in one cross-sectional image taken in a direction orthogonal to the surface direction of the high-frequency circuit board. It is calculated by averaging the values (parts). When the average thickness of the aforementioned wiring is 1.0 μm or more, it can transmit electrical signals and is suitable for use as a circuit board. When the average thickness of the wiring is 40 μm or less, it is suitable for use as a flexible circuit board.

When the width of the wiring is 50 μm or less, examples of the wiring forming method include SAP (Semi Additive Process) and MSAP (Modified Semi Additive Process). The aforementioned SAP and the aforementioned MSAP can be suitably used to form fine circuits.

Although there is no particular limitation on the method of forming the wiring, subtractive technology methods other than SAP (Semi Additive Process) and MSAP (Modified Semi Additive Process) are exemplified.

<Other layers>

Examples of the aforementioned other layers include an oxidation prevention layer, an anti-rust layer, and the like.

<<Oxidation prevention layer>>

The oxidation prevention layer is a layer disposed on the surface where the wiring and the adhesion layer are exposed.

The oxidation prevention layer is the same as that described for the conductive film for high-frequency circuit boards.

<<Anti-rust layer>>

The anti-rust layer is a layer disposed on the exposed surface of the wiring and the adhesion layer, or on the exposed surface of the oxidation prevention layer in the wiring.

The shape, structure, and size of the rust-proof layer are not particularly limited and can be appropriately selected depending on the purpose.

Examples of materials for the anti-rust layer include benzotriazole-based, imidazole-based, thiol-based compounds, and the like.

The anti-rust layer can be formed on the exposed surface of the wiring and the adhesion layer by wet plating, immersion plating, spray plating, or the like, or can be disposed on the exposed surface of the oxidation prevention layer in the wiring. .

The transmission loss of the high-frequency circuit board of the present invention is preferably -10dB/100mm or more at a frequency of 40 GHz, more preferably -9dB/100mm or more, and more preferably -8dB/100mm or more.

For the transmission loss of high-frequency circuit boards, microstrip lines are formed on various substrates, and the circuit line width and the average thickness of the aforementioned wiring are adjusted to make the impedance of the circuit comply with 50Ω. Impedance and transmission loss can be measured to 40GHz using a network analyzer (manufacturer: KEYSIGHT TECNOLOGIES, model: E8363B) using a probe.

The high-frequency circuit board of the present invention sequentially includes: the aforementioned base material, the aforementioned adhesion layer, the aforementioned wiring, and the aforementioned other layers.

Here, an example of the high-frequency circuit board of the present invention will be described with reference to the drawings.

FIG. 2A is a cross-sectional view showing an example of the high-frequency circuit board of the present invention. The high-frequency circuit board 20 shown in FIG. 2A includes an adhesion layer 12 and wiring 14 on a base material 11 in this order.

FIG. 2B is a cross-sectional view showing another example of the high-frequency circuit board of the present invention. The high-frequency circuit board 20 shown in FIG. 2B includes an adhesion layer 12, a wiring 14, and an oxidation prevention layer 15 on the base material 11 in this order. The oxidation prevention layer 15 is disposed to cover the exposed surfaces of the adhesion layer 12 and the wiring 14 .

FIG. 2C is a cross-sectional view showing another example of the high-frequency circuit board of the present invention. The high-frequency circuit board 20 shown in FIG. 2C includes an adhesion layer 12, a wiring 14, and an anti-rust layer 16 on the base material 11 in this order. The anti-rust layer 16 is disposed to cover the exposed surfaces of the adhesion layer 12 and the wiring 14 .

FIG. 2D is a cross-sectional view showing another example of the high-frequency circuit board of the present invention. The high-frequency circuit board 20 shown in FIG. 2D includes an adhesion layer 12, a wiring 14, an oxidation prevention layer 15, and an anti-rust layer 16 in this order on the base material 11.

[Example]

Hereinafter, although the Example of this invention is demonstrated, this invention is not limited to these Examples.

(Example 1)

<Manufacturing of conductive film 1 for high-frequency circuit boards>

After pre-processing the top of a cycloolefin polymer (COP) diaphragm (base material, manufactured by Japan ZEON Corporation, product name: ZEONOR) with an average thickness of 100 μm , a nickel-copper alloy containing 35% by mass copper was used as the material. By introducing argon gas and performing sputtering, an adhesion layer with an average thickness of 10 nm is formed.

Next, with argon gas introduced, copper was used as a material and sputtered on the adhesion layer to form a copper layer with an average thickness of 120 nm, thereby obtaining the conductive film 1 for a high-frequency circuit board.

(Examples 2 to 8 and Comparative Examples 1 to 2)

In Example 1, conductive films 2 to 10 for high-frequency circuit boards were manufactured in the same manner as in Example 1, except that the type of base material and the type of adhesion layer were changed as shown in Table 1.

Next, the average thickness of each layer in the conductive film for high-frequency circuit boards is measured as follows.

-Average thickness of adhesion layer and copper layer-

First, a circuit board is prepared. A plurality of adhesion layers or copper layers with a specific thickness are formed on the circuit board. The physical film thickness of a plurality of adhesion layers or copper layers with a specific thickness is measured through a contact profilometer. Next, through quantitative analysis using a fluorescent X-ray measurement device (XRF), the amount of adhesion layer or copper layer material in a plurality of adhesion layers or copper layers with specific thicknesses is measured. The aforementioned film thickness is measured by a contact profilometer, and the amount of the adhesion layer or copper layer material is measured through quantitative analysis using a fluorescent X-ray measuring device (XRF) to form a calibration line. Quantitative analysis of the conductive film for high-frequency circuit boards using a fluorescent as the average thickness.

Regarding the average thickness of the copper layer, the measurement is carried out in the same manner as the average thickness of the adhesion layer, except that the copper from the copper layer is detected and the average of the measurement values of 10 parts is used as the average thickness. The results are as follows As shown in Table 1.

In addition, the relative permittivity and loss tangent of the substrate were measured at a frequency of 10GHz based on the resonant cavity method based on JIS R1641. The results are shown in Table 1.

The surface roughness of each base material was measured using an optical interference surface roughness meter manufactured by Bruker Japan Co., Ltd. (model: WYKO ContourGT K1M, measurement conditions: VSI mode).

In addition, the optical properties of each base material were measured according to JIS K7361-1/Haze: JIS K7136, using a haze meter (manufactured by Nippon Denshoku Industry Co., Ltd., model number: NDH5000SP) to measure the total light transmittance. The results are shown in Table 1.

In addition, the composition of the adhesion layer is measured using an X-ray photoelectron spectrometer (XPS, ESCA, manufactured by ULVAC-PHI Co., Ltd., model: model 5400) by analyzing the element concentrations of nickel, chromium, and copper in the adhesion layer. The results are shown in Table 2.

Next, regarding the obtained conductive film for high-frequency circuit boards, "etchability", "adhesion strength" and "transmission loss" were evaluated as follows. The results are shown in Table 3.

<Etching property>

Put 1% ferric chloride (liquid temperature: 23°C) into a glass beaker, immerse the conductive diaphragm of the high-frequency circuit board into it, take it out after 180 seconds, and then rinse with water. Wipe off the moisture with KIM TOWEL wipes and visually check for the presence of residue and evaluate based on the following evaluation criteria.

[Evaluation criteria]

No residue: O

There is residue:X

<Adhesion strength>

First, the copper layer (copper sputtering) surface was cleaned with dilute sulfuric acid, and then electroplated in a copper sulfate aqueous solution to obtain a wet electroplated copper layer with an average thickness of 20 μm , which was used as a test sample. Using the obtained test sample, the adhesion strength was measured according to the following measurement method.

-Measurement method-

On a 10 cm square copper layer (copper sputtering) sample, a copper layer with an average thickness of 20 μm was formed by electrolytic plating, and then cut into a width of 5 mm. Attach the sample to the mounting board with double-sided tape. Fix the base material part fixed to the board on the lower fixture, and install the part of the adhesion layer and wet electroplated copper layer that has been peeled off on the upper fixture. Use a precision universal testing machine (Shimadzu Corporation) to measure the current load capacity at a speed of 50mm/min and a stretching direction of 180 degrees.

<Transmission loss>

On the copper layer (copper sputtering) in the obtained conductive film for high-frequency circuit boards, a microstrip line was formed using subtractive technology, a high-frequency circuit board was manufactured, and the transmission loss was measured. Adjust the circuit width and plating thickness to make the circuit impedance comply with 50Ω. The impedance and transmission loss were measured to 40GHz using a network analyzer (manufacturer: KEYSIGHT TECNOLOGIES, model: E8363B) using a probe and evaluated. The results are shown in Table 3 and Figure 3. In addition, regarding Examples 5-8, the transmission loss was not measured.

10: Conductive diaphragm for high frequency circuit boards

11:Substrate

12:Adhesion layer

13: Copper layer

Claims (4)

A conductive film for high-frequency circuit boards, characterized in that it sequentially includes: a base material; an adhesion layer provided on at least one side of the base material; and a copper layer provided above the adhesion layer; wherein, at 10 GHz At the measurement frequency, the relative permittivity of the base material is 3.3 or less; the adhesion layer includes a nickel-copper alloy, and the average thickness of the adhesion layer is between 3 nm and 50 nm. The conductive film for high-frequency circuit boards according to claim 1, wherein the base material includes at least any one of cycloolefin polymer resin, polyphenylene sulfide resin, polystyrene resin, fluororesin and polyether ether ketone resin. One kind. The conductive film for high-frequency circuit boards according to claim 1 or 2, wherein the adhesion strength of the interface between the base material and the adhesion layer is 0.5 N/mm or more. A high-frequency circuit board, characterized by sequentially comprising: a base material; an adhesion layer provided on at least one side of the base material; and wiring provided above the adhesion layer; wherein, at a measurement frequency of 10 GHz, The relative permittivity of the base material is 3.3 or less; the adhesion layer includes a nickel-copper alloy, and the average thickness of the adhesion layer is 3 nm or more and 50 nm or less.